The present invention relates to a liquid chromatograph mass spectrometer (hereinafter referred to as LC/MS).
In the LC/MS, an interface is used in order to ionize a liquid sample separated and eluted from a column of a liquid chromatograph (LC) section corresponding to a retention time, and introduce the ion into a mass spectrometer (MS) section. The interface includes an ionizing device for generating ions while atomizing gas ions, by utilizing means for heating, a high-speed air flow, a high electric field or the like. The interface also includes an ion lens which suitably focus ions, and accelerate ions to be sent to subsequent sections, if necessary.
In order to improve a sensitivity for analyzing by the LC/MS, it is important for the ionizing device as described above to ionize the liquid sample effectively, namely to improve the efficiency of generating the ions. It is also important to introduce ions into a mass separator effectively, for example quadrupole filter, namely to improve the passing efficiency of ions into the mass separator. To achieve the improvement, it is necessary that conditions, such as a temperature of each part of the interface and impressed voltage, are set appropriately.
In the conventional LC/MS, when a standard sample including a defined content is introduced into a mass separator through the interface, the applied voltages to the respective parts, such as the ion lens, are adjusted so that the number of ions which reach an ion detector may be maximum, concretely a peak of a mass spectrum corresponding to the defined content becomes highest. In fact, however, the conditions where ions pass through most effectively also depend on the number of ions. Therefore, in case that a scanning measurement is carried out in a designated mass range, the impressed voltages of the parts, such as the ion lens, is not always most suitable for passing of the ions. This is one of the reasons that the sensitivity and an accuracy of detection become worse.
The present invention has been made in order to solve the foregoing problems, and an object of the invention is to provide a liquid chromatograph mass spectrometer in which the sensitivity and accuracy of the detection are improved by introducing object ion into the mass separator section effectively.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To solve the aforementioned problems, the present invention provides a liquid chromatograph mass spectrometer having an interface, which includes an ionization chamber, in which a liquid sample supplied from a liquid chromatograph portion is atomized and ionized at about an atmospheric pressure, and a generated ion in the ionization chamber is introduced into a mass separator under high vacuum condition through a first intermediate chamber and a second intermediate chamber.
The liquid chromatograph mass spectrometer includes a solvent removing tube disposed in the interface for carrying a droplet including the ion from the ionization chamber to the first intermediate chamber; a first ion lens disposed in the first intermediate chamber, and having a plural of board electrodes arranged along an ion optical axis c; a second ion lens disposed in the second intermediate chamber, and having 2n rod electrodes, n being an integer and at least two, which is arranged along the ion optical axis c; first voltage generation means for applying direct current to the solvent removing tube; a second voltage generation means for applying high frequency voltage superposed on the direct current voltage to the board electrodes; a third voltage generation means for applying high frequency voltage superposed on the direct current voltage into the rod electrodes; a memory means for storing voltage data for the solvent removing tube, the first ion lens and the second ion lens corresponding to a mass number so that an efficiency of passing of the ions becomes best; and control means for controlling the first, the second and the third voltage generation means so that the voltages based on the voltage data which are stored by the memory means can be applied to the solvent removing tube, the first ion lens and the second ion lens when an appropriate voltage corresponding to a mass number of the sample is applied to the mass separator.
In the liquid chromatograph mass spectrometer of the invention, for example, the applied voltages to the solvent removing tube, the first ion lens and the second ion lens are respectively studied in advance with respect to each mass number by analyzing one or a plurality of standard samples including a plurality of different components which have different mass number so that an efficiency of passing of ions becomes best. Based on the results of the study, voltage scanning patterns for determining the best or almost the best applied over a whole range of the mass numbers which can be analyzed, are made and stored in a memory portion.
When a scanning measurement is carried out, the voltage is applied or scanned to the mass separator so that the ions having the specific mass number, which are the subject of analyzing, may only pass through in sequence. Control means changes the applied voltage to the solvent removing tube, the first ion lens and the second ion lens by controlling the first, the second and the third voltage generating means according to the voltage scanning patterns stored in the memory section, synchronizing with the scanning of the applied voltage with respect to the mass separator. The ions in the best or almost the best condition pass through the path from the entrance of the solvent removing tube to the mass separator by the control means. Accordingly, more ions are introduced into the mass separator and the number of the ions reaching to the ion detector increases.
Incidentally, the voltage scanning patterns as described above have almost fixed shapes of straight lines or curve lines. It is desirable that pattern making means, which makes the voltage scanning pattern by suitably complementing between the plural scattered data given by measuring the standard sample, according to a designated algorithm, is provided. In the pattern making means, although there are few points of the mass numbers measured in advance, almost the best voltage scanning pattern can be made. Therefore, more appropriate voltage can be applied to the solvent removing tube, the first ion lens and the second ion lens.
According to the liquid chromatograph mass spectrometer of the present invention, since the efficiency of introducing the objective ion into the mass separator is improved regardless of the mass number of the ion, the efficiency of the detection of the ions by the ion detector is improved. Accordingly, the accuracy and sensitivity of the analysis by using the mass spectrometer is improved, and a repeatability is also improved.